The present invention relates to a reception circuit and an adaptive array antenna system using the same and, more particularly, to a reception circuit and adaptive array antenna system which can accurately control a propagation delay phase difference at a reception section for a reception signal.
As a receiver antenna, an adaptive array antenna is available, whose beam can be electronically directed in the arriving direction of radio waves, i.e., whose directivity can be adjusted. This adaptive array antenna is widely used as an antenna suited to mobile reception, and various types of adaptive array antennas have been proposed. In general, an adaptive array antenna system has a plurality of antenna elements and is designed to obtain a desired reception signal by synthesizing outputs from reception circuits provided for the respective antenna elements.
Each of the conventional reception circuits serving as preprocessing sections combined with the respective antenna elements of the above adaptive array antenna includes an oscillator for a local oscillation signal. In this case, the respective oscillators are not necessarily consistent with each other in terms of phase, and there are phase errors between local oscillation signals. For this reason, when frequency conversion is performed by a mixer in each radio signal reception section (to be referred to as a reception section), the corresponding phase error is added to the reception signal. However, each signal after addition varies in passing phase at the corresponding reception circuit. That is, this phase is not fixed. It is therefore impossible to detect a propagation delay phase difference upon reception by the antenna at the subsequent stage.
As described above, a propagation delay phase difference in each reception circuit is not controlled. For this reason, in an adaptive array antenna or the like designed to operate by using a plurality of reception circuits at once, in particular, a random propagation delay phase different in each reception circuit directly influences the performance of the apparatus in use. That is, when reception circuits are used for an adaptive array antenna system or the like, since a propagation delay phase difference of a reception signal cannot be accurately calculated, correction and the like cannot be performed. If, therefore, a propagation delay amount in each reception circuit can be managed and controlled, the apparatus performance can be improved.
As one of the measures against such a problem, a shared synthesizer scheme may be provided. For example, an example of this arrangement is disclosed in Japanese Patent Laid-Open No. 10-224138. In this type of adaptive array antenna system, however, oscillators equal in number to channels must be prepared. In addition, since signals must be distributed to the respective reception circuits through a coaxial cable or the like, the apparatus becomes bulky.
It is an object of the present invention to provide a reception circuit and adaptive array antenna system which can accurately reproduce the propagation phase delay characteristics of a reception signal.
It is another objet of the present invention to provide a reception circuit and adaptive array antenna system which have small-scale circuit configurations with small changes as compared to a conventional circuit.
In order to achieve the above objects, according to the present invention, there is provided a reception circuit comprising a reception section for performing frequency conversion of an input signal by using a local frequency signal generated by phase comparing operation, and a control section for removing a passing phase error, added in the reception section, on the basis of a phase comparison signal output from the reception section.